Whats the best way to make smooth waterslide type tracks?
Create a bezier circle. Go into the curve properties, and increase the Extrude property.

Go into edit mode, select all the control points with A and set the tilt to 90°. (Press N to open the right hand panel if it is closed)

Tweak the tilt of each control point to have some kind of curvature.

Add a solidify and edge split modifier to get depth.

Select two control points and richt click &gt; Subdivide to add a new one between the two. Tweak them, tilt them to your liking.

Adjust the resolution units to keep the poly count low

If you want a custom profile, add a bezier curve

And use it as your bevel object

Result : 676 verts